Transmit Power Control Algorithms for Sources and Sinks in a Multi-Link Session

ABSTRACT

Transmit power control functionality in wireless audio systems may be implemented by way of a Transmit Power Control (TPC) algorithm devised to control power for both source and sinks in a multi sink session, to reduce power consumption. Information may be passed back and forth between the source and sink devices to adjust power based on the shared information. The TPC algorithm may allow power control on both ends of an RF link, and may have multiple sink devices communicating with a source device. Furthermore, the multiple sink devices and the source device may each be operating at different power levels, and adjust their respective power levels as instructed by the TPC algorithm. Power control is therefore implemented on both ends of the link, where multiple sources and sinks may all operate at different power levels, and all individually adjust their respective power levels.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to RF transceiver design, and, more particularly,controlling the output power of an RF transmitter.

2. Description of the Related Art

Radio frequency (RF) transmitters/receivers are used in a wide varietyof applications, including wireless network interfaces, mobiletelephones, and Bluetooth interfaces. RF transceivers also featureprominently in wireless audio technology directed to headphones andearphones, home audio/theater systems and speakers, portable audio/mediaplayers and automotive sound systems. Robust, high-quality audio andlow-power RF capability can make it possible for consumer and automotiveoriginal equipment manufacturers (OEMs) to integrate wireless audiotechnology into portable audio devices and sound systems. Overall,various RF technologies lend themselves to a number of applications inthe consumer world to create high-fidelity home theater environments anddistribute audio in the home and other environments.

A radio communication system typically requires tuned circuits at thetransmitter and receiver, all tuned to the same frequency. Thetransmitter is an electronic device that propagates an electromagneticsignal, representative of an audio signal, for example, typically withthe aid of an antenna. An RF transceiver is designed to include both atransmitter and a receiver, combined to share common circuitry, manytimes appearing on the same piece of integrated circuit (IC) chip. If nocircuitry is common between transmit and receive functions, the combineddevice is referred to as a transmitter-receiver. Transceivers usuallycombine a significant amount of the transmitter and receiver handlingcircuitry.

RF Transceivers use RF modules for high-speed data transmission. Thecircuits in a digital RF architecture can operate at frequencies of upto 100 GHz. In most systems, digital processors or processing elements(which are oftentimes software-programmable) are used to performconversion between digital baseband signals and analog RF, andoscillators are used to generate the required periodic signals. Many RFcircuits make use of a voltage-controlled oscillator (VCO), in which theoscillation frequency is controlled by a voltage input, and theoscillation frequency is controlled through an applied DC voltage.Another common element of RF transceivers is the RF power amplifier,which is a type of electronic amplifier used to convert the low-power RFsignal into a larger signal of significant power, typically for drivingthe antenna of the transmitter. RF amplifiers are usually designed tohave high efficiency, high output Power compression, good return loss onthe input and output, good gain, and optimum heat dissipation.Oftentimes, however, wireless audio systems also have a high demand forlow power operation, for example when operating on battery power. Inorder to prolong the battery life of such a wireless audio system, it isdesired to improve the power efficiency of the system.

Other corresponding issues related to the prior art will become apparentto one skilled in the art after comparing such prior art with thepresent invention as described herein.

SUMMARY OF THE INVENTION

In one set of embodiments, a wireless audio system (which may beimplemented as an integrated circuit, or chip) having a transmit pathand a receive path may be operating on a high frequency band, e.g. a 2.4GHz frequency band. A Radio Frequency Power Amplifier (PA) in thetransmit path may provide the RF power for signals to be transmittedthrough an antenna over the air to a corresponding receiver, which mayinclude its own receive path. The RF signal loss in the air may varyconsiderably. In order to allow the system to operate at a higher pathloss, higher output power of the PA may be desired. However, in typicalRF designs, any increase of the maximum PA output power may cost asignificant increase in the power consumption. Power efficiency may beimproved by introducing transmit power control functionality in thewireless audio system. While the RF transmit power block usuallyconsumes most power in a wireless system, it is not always necessary forthe wireless audio system (or chip) to operate at the highest RF power.When the channel path loss or channel interference is not high, thetransmit PAs may not need to operate at the highest power operationpoint. The PAs may actually be biased at a lower current point to obtaina lower output power and current of the PA.

To improve coexistence (with nearby devices) and further reduce powerconsumption, transmit power control functionality may be implemented byway of an algorithm devised to control power for both source and sinksin a multi-sink session. Information may be passed back and forthbetween source and sink devices to adjust power based on the sharedinformation. Different devices with different power levels may be ableto adjust for the power levels of the other source and sink devices, andsinks may also have multiple levels of transmit power (multiple transmitpowers) and adjust to operate correctly.

The transmit power control (TPC) algorithm may allow power control onboth ends of an RF link, and may have multiple sink devicescommunicating with a source device. Furthermore, the multiple sinkdevices and the source device(s) may each be operating at differentpower levels, and adjust their respective power levels as instructed bythe TPC algorithm. In other words, power control is implemented on bothends of the link, where multiple sources and sinks may all operate atdifferent power levels, and all individually adjust their respectivepower levels. The different source and sink devices may also adjusttheir respective power levels in a unified way so they can allcommunicate with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing, as well as other objects, features, and advantages ofthis invention may be more completely understood by reference to thefollowing detailed description when read together with the accompanyingdrawings in which:

FIG. 1 shows the partial block diagram of one embodiment of a RadioFrequency (RF) system including a host system;

FIG. 2 shows the partial block diagram of one embodiment of an RFtransceiver system including a Power Management and Audio (PMA) blockand an RF transceiver and Baseband Processing (RBP) block;

FIG. 3 shows the partial block diagram of one embodiment of the Radioportion of the RPB block of the RF transceiver system of FIG. 2;

FIG. 4 shows the partial block diagram of one embodiment of the digitalcore of the RPB block of the RF transceiver system of FIG. 2;

FIG. 5 a shows a partial circuit diagram of one embodiment of the PowerControl block in the embodiment of Radio portion of the RPB block inFIG. 3;

FIG. 5 b shows a partial circuit diagram of one embodiment of the PowerControl block in the embodiment of Radio portion of the RPB block inFIG. 3 for extended range power amplification;

FIG. 6 shows the flowchart for one embodiment of a source side transmitpower control algorithm;

FIG. 7 shows the flowchart for one embodiment of a sink side transmitpower control algorithm;

FIG. 8 a shows a table containing description of the state variables ofthe flow chart in FIG. 6; and

FIG. 8 b shows a table containing description of the state variables ofthe flow chart in FIG. 7.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims. Note, the headings are for organizational purposes only and arenot meant to be used to limit or interpret the description or claims.Furthermore, note that the word “may” is used throughout thisapplication in a permissive sense (i.e., having the potential to, beingable to), not a mandatory sense (i.e., must). The term “include”, andderivations thereof, mean “including, but not limited to”. The term“coupled” means “directly or indirectly connected”.

DETAILED DESCRIPTION

FIG. 1 shows the partial block diagram of one embodiment of a wirelessaudio system that includes a Radio Frequency (RF) transceiver system 100divided into two main functional components: a Power Management andAudio (PMA) block 114 and an RF Transceiver and Baseband Processing(RBP) block 116. PMA 114 and RBP 116 may each be configured on anIntegrated Circuit (IC) or on respective ICs, and may interface witheach other via a number of signals (more details of RF transceiversystem 100 are shown in FIG. 2 and are discussed in more detail below).PMA 114 and RBP 116 may also couple to components of a host system 110through a host bus interface (HBI) 102. Host system 110 may include oneor more memory elements 104 that can store program code executable by aprocessing unit 106 (which may be a general purpose central processingunit, or a microcontroller or some similar component) to perform variouscontrol operations on RF transceiver system 100. In turn, RF transceiversystem 100 may provide certain feedback signals to host system 110 forbidirectional communication between RF transceiver system 100 and hostsystem 110. In some embodiments, RF transceiver system 100 may bedesigned to be self contained, and perform independently all or mostfunctionality required for RF transceiver system 100 to operate. Forexample, in one embodiment, RBP 116 may include a microcontroller andmemory elements to perform functions that may otherwise be performedunder the control of host system 110, and thereby not require hostsystem 110 for performing the necessary RF functions.

As mentioned above, RF transceiver system 100 may include two maincomponents, PMA 114 and RBP 116. PMA 114 itself may include two mainblocks as shown in FIG. 2. The first block is a Power Management Block(PMB) 206, and the second block is and Audio Output Path (AOP) 214. PMA114 may further include a couple of smaller blocks, specifically a PowerOn Reset (POR) block 208, and a Serial Peripheral Interface (SPI) 212 toexchange data and information with RBP 116. PMB 206 and AOP 214 may bekept functionally separate, though they may be joined by running the AOPsupply with the PMB by using a circuit board connection. PMB 206 mayinclude a DC-DC converter, Battery Charger and Button Control Circuitry(not shown/detailed in FIG. 2). In one set of embodiments, AOP 214converts serial audio data received via SPI 112 into an analog audiosignal, and amplifies the analog audio signal using a high efficiency,class-D headphone driver. RBP 116 may include a Radio Transceiver block218, a Digital Baseband and Processing component 226 (which may includea CPU and/or Microcontroller, as well as memory elements/registers), aPOR block 220, and an SPI 224 to exchange data and information with PMA114.

The state of PMA 114 may be controlled by digital input data throughregister writes. The digital input data may be delivered as lowduty-cycle data, and may be provided into a register bank (not shown)inside PMA 114 by way of SPI 212. Since SPI 212 may be a bidirectionalinterface, it may also be used to read the state of the register bank.This capability may facilitate the reading of low duty-cycle digitaloutputs for the purpose of testing. The digital circuitry in PMA 114 mayoperate on two clock domains. The incoming SPI_CLK may be used to clockdata into an SPI Receive FIFO (not shown) within SPI 112, and out of theSPI Transmit FIFO (not shown) also within SPI 212. The remainder of thedigital circuitry, which may include registers, Finite State Machines,the Read Port of Receive FIFO, and the Write Port of the Transmit FIFO)may be clocked by an internal clock (Mclk). The core of SPI 212 may beused to retime signals between the two clock domains. The reset for thecircuitry SPI 212 may be completely asynchronous, in which case no clockis used during reset. Registers may reset to their default values, toensure that analog components remain inactive. The circuitry of SPI 212(and also that of FSMs) may remain enabled (i.e. it may reset to anenabled state), while the clocks may run during SPI operations.

PMA 114 may receive a specified digital audio signal, e.g. a 16-bitPulse Code Modulated (PCM) audio signal through its serial audio port.The digital audio data may be digitally filtered and up-sampled to aspecified Audio CLK frequency, and modulated by Multi-loop Noise Shaping(MASH) in the digital audio codec. In some embodiments, the MASH may bea 2-1, 4-bit implementation. The filtered, up-sampled, and modulateddata (in case of a 4-bit implementation, the 4 data bits) may drive theinput of a dynamic element matcher (DEM), the output of which may beprovided to an analog section of PMA 114. PMA 114 may be implementedwith four clock domains. The four clocks may include a master clockMclk, an audio clock AudioClk, a DC-DC converter clock clkDCDC, and anSPI clock SPI_CLK. All clocks may be derived from a specified crystalfrequency (e.g. 22.5792 MHz, in some embodiments), or an audio clockPhase Locked Loop (PLL) output frequency (e.g. 24.576 MHz in certainembodiments). The AudioClk may be derived by passing the Mclk through adivide-by-two circuit. The AudioClk may drive the DEM and the audiodigital to analog converter (DAC). Mclk may be generated by the systemclock of RBP 116. Mclk may also be used for much of the digital SPIcircuitry, including all registers and any SPI FSM. The branch of theclock tree provided to SPI may be gated, and may toggle only during SPIdata transfers. The SPI clock may be synchronous with the Mclk,. TheDC-DC converter clock may be synchronous to the Mclk, and may default tothe AudioClk frequency, to mix power supply noise, possibly generated bythe DC-DC converter block within PMB 206, to DC, in order to eliminateany negative impact on audio dynamic range.

PMA 114 may power up in a low power mode, in which all analog blocks maybe disabled, and digital components/circuitry may not be toggling. Toaccomplish this, POR block 208 within PMA 114 may generate a POR signalthat forces PMA 114 into a known low power state as soon as the supplyvoltage VDD3V is valid. Note that in order to simplify the block diagramin FIG. 2, clkDCDC and AudioClk are not shown. During power-up the DC-DCconverter may be in full standalone mode, its clock generated locally atstart-up. In general, the DC-DC clock may not be involved with thedigital core of PMA 114. PMB 106 may be standalone to provide the choiceof using either external charger and DC-DC converter, or onboard/on-chipcharger/DC-DC converter for battery charging and switching regulatorfunctions. The user may also have the option of using onboard/on-chipDC-DC and external charger, in case batteries other than Li+ ionbatteries are used. The functionality of PMB 106 may be controlledthrough a software algorithm, which may be executed for example byprocessing unit 106 of FIG. 1, or the CPU inside Digital Baseband andCPU block 226 of RBP 116, or possibly by a microcontroller/processingelement within PMB 206.

In various embodiments, AOP 214 may include a Class-D headphone driverfeaturing a switching amplifier that uses Natural Sampling Pulse WidthModulation (PWM) to convert an analog input into a series ofRail-to-Rail pulses. The audio signal may be encoded in the averagevalue of the PWM pulse train and may be recovered from the PWM signal byanalog low pass filtering at the headphone. Switching amplifiers areknown to be efficient (especially if zero voltage switching techniquesare used) since voltage drop across the amplifier output stage can bekept low while delivering current to the load. However, switchingamplifiers are also known to have impairments that degrade linearity andsignal to noise ratio (SNR). Specifically, power supplypushing/glitching and crossover distortion are signal dependentnon-idealities that contribute to total harmonic distortion (THD) inaudio Class-D amplifiers. In one set of embodiments, a Class-D headphonedriver may be designed with a negative feedback network to compare theoutput signal with the input signal and suppress non-idealitiesintroduced by the Class-D switching stage, and may perform 2^(nd) ordernoise shaping via the DEM element (not explicitly shown) to reduce noiseat low power operation.

FIG. 3 shows the circuit diagram of one embodiment of Radio block 218from RPB 116. The embodiment shown in FIG. 3 includes a transmitterstage 300, and a receiver stage 301. A transmit “I” and a transmit “Q”signal are provided from digital baseband circuitry 304 todigital-to-analog converters (DACs) 306 and 308, respectively, fortransmission via amplifier circuitry 316 operating under power control318. Quadrature modulation is performed by mixers 312 and 322, which areoperated according to quadrature signals based on the output ofTransmitter Local Oscillator (TxLO) 332, fed through phase shifter 324to provide the quadrature phase shift. The outputs from DAC 306 and DAC308 each pass through respective RC filters 310 and 320 before reachingrespective mixers 312 and 322. A reference clock generation circuit 336is used to provide a square wave signal as first base frequency F₀ (e.g.a low frequency of approximately 22.5 MHz) periodic signal tophase-locked loop (PLL) 330. Circuit 336 is also used to provide a basefrequency F_(out) periodic signal to digital baseband circuitry 304.TxLO 332 may be an injection locked oscillator controlled from PLL 330.Any numeric values provided with respect to the RF system shown in FIG.3 are exemplary, and various embodiments are not meant to be limited tothe specific values provided herein. In one set of embodiments, powercontrol block (PCB) 318 may be configured to execute a transmit powercontrol algorithm to control power on both source and sink sideoperation of transmitter stage 300.

In one embodiment, RBP 116 is divided into three functional portions:Digital and Analog IO Pads, Analog Design blocks, and a Digital Core.RBP 116 may have two main “modes” of operation: a Source Mode and a SinkMode. Source and Sink Mode are in reference to the direction of audiotravel, but may also be indicative of the clock synchronization. ASource device may receive an audio stream from an external audio source,and send it to a Sink device over a wireless interface. The Sink device,in turn, may pass the audio stream out to a destination. From a clocksynchronization perspective, the Source device may contains the “Master”clock and the Sink device may synchronize its oscillator to that Masterclock. The Source device may also possibly further synchronize to anexternal clock signal, but such synchronization would not affect Sourceand Sink functionality.

With respect to Source and Sink devices, the expressions “Ingress” and“Egress” are oftentimes used. Ingress refers to the direction of datatowards the wireless interface, and Egress refers to circuitscontrolling or processing data flowing away from the wireless interface.For example, a Source chip may therefore carry Ingress Audio, while aSink chip may carry Egress Audio. A simplified diagram of one possibleSource and Sink pairing is shown in FIG. 4. Blocks 402 and 404 arepartial block diagrams showing the high level organization of certainfunctional blocks in one embodiment of the digital core of RPB 116,operating as a Source. Similarly, blocks 408 and 406 are partial blockdiagrams showing the high level organization of the functional blocks inthe same embodiment of the digital core of RPB 116, operating as a Sink.Source and Sink pairing may be established over wireless (RF) interface410. The functional blocks within blocks 402 and 406 representfunctional groups.

As listed in FIG. 4, the digital functional groups may include DigitalBaseband components, Voice Path components, Audio Path components,Microcontroller components, and Device Core Function components. Ingressdirection is towards the device pins from the transmit basebandcomponents, specifically from transmit baseband 420 to pins 404, andfrom transmit baseband 430 to pins 408. Conversely, Egress direction isfrom the pins to the receive baseband components, specifically from pins404 to receive baseband 422, and from pins 408 to receive baseband 432.In one set of embodiments, the voice path may be full duplex, i.e., bothdirections may operate at the same time, while the Audio path may onlybe receiving or transmitting to the Radio during a mode of operation.The Audio may be transmitting to the Radio in Source Mode and may bereceiving in Sink Mode. As mentioned above, data path directions arereferred to herein as Ingress and Egress with the Radio (RF transceiver)operating as the reference point.

As shown in FIG. 4, RBP 116 may contain several core functions,illustrated in devices 402 and 406. These core functions may be used tofacilitate operation of the higher level data path functions. Examplesof this include selecting PAD functionality, reset functions and clockfunctions. The audio path may take audio data from a Source/IngressDevice Serial Audio Interface (SAI) and may transport it to aSink/Egress Device and out through the Sink/Egress Device SAI.Programmability may be available on the external audio interfaces(external SAI) of both devices to allow the SAI to interface with avariety of external devices. The Audio Path may also employ a number ofstrategies to handle power, latency and interferences issues. The Voicepath may be bidirectional. It may allow full duplex voice communicationacross the devices. Each device (such as device 402 and 406) may have aningress voice path that takes voice data from its programmable SerialVoice Interface (SVI) and may transport it to its paired device, fromwhich it is sent out the egress SVI. This path may employ a number ofstrategies to handle power, latency and interferences issues. TheMicrocontroller may support several interfaces, such as GPIO, SPI, TWI,etc.

The Digital Baseband may provide the digital portion of the RFTransceiver. In the ingress direction it may take the digital signalingand process it to be sent to the analog portion of the RF Transceiver.In the egress direction, it may process the signal and recover theoriginal packet created by the ingress radio. The ingress DigitalBaseband is referred to as the TX Baseband, and the egress direction itis referred to as the RX Baseband. The Sequencer and TimeSynchronization Function (TSF) are functions of the Baseband that allowautomation and synchronization of both Basebands relative to theirpaired device.

Transmit Power Control

As shown in FIG. 3, the transmit amplifier (and pre-amp when applicable)may be under control of a Power Control block 318. Transmit powercontrol is performed to control the PA output power to improve the powerconsumption of the system. In one set of embodiments, two differentsystems applications may feature different PA power control mechanisms.A first system may include module PA power control, and a second systemmay include an extended range PA power control. FIG. 5 a shows the basicblock diagram of one embodiment of a module PA output power controlblock 504, which may represent one embodiment of Power Control block 318together with amplifier 316. The output power level of PA 316 may beadjusted by digital circuitry 516, which may generate a control signalpassing via DAC 514 and Low Pass Filter (LPF) 512, mixed by mixer 510using oscillator 508. In one set of embodiments, the power level may beadjusted in specified step increments, from a specified lowest value toa specified highest value. For example, the output power of PA 316 maybe adjusted in 5 dBm increments from −40 dBm to −5 dBm, and from therebetween −2 dBm and +2 dBm using another specified step size. The powerlevels may vary between various different specified embodiments of RBP116 (or between various different devices as exemplified by deviceblocks 402 and 406 in FIG. 4.

An embodiment of an extended range PA power control block 524 is shownin FIG. 5 b, and includes an additional, external PA 518 to boost theoutput RF power of the module up to a specified value, e.g. 20 dBm. Thehigher output RF power may enable devices that implement it to work overgreater distances than devices that use only PA 316. However, the addedexternal PA 518 may also consume a great deal of power. Both the modulePA power control and extended range PA power control, including controlof external PA 518 may be performed via an internal Microcontrollerexecuting programming instructions within the Digital Baseband and CPUblock 226 shown in FIG. 2, and also in devices 402 and 406 as part ofthe Microcontroller Path components. In that case, Digital Circuitry 516is meant to reference those components as being responsible forgenerating the control signal provided to DAC 514. In order to savepower, PA 316 may be set to a lower level whenever possible. For someembodiments, this may require power control on both Sink (SNK)transmitters and Source (SRC) transmitters. Extended range applicationsemploying an external PA (e.g. PA 518) may result in a slightlydifferent Transmit control algorithm implementation for module PA powercontrol and extended range PA power control.

Transmit Power Control Algorithm

In one embodiment of a Transmit Power Control (TPC) algorithm, the SRCmay determine the desired SRC power level by measuring the receivedsignal (from SNK) level, and indirectly measuring the path loss. The SRCmay assume that the path loss is the same for both paths, i.e. forSNK-SRC and SRC-SNK. In one embodiment, power control is only performedon the SRC because the SNK may be in transmit mode for less than 10% oftime, which means that Transmit power control may have minimal impact onoverall power consumption. As mentioned above, PA 316 may have aspecified number of steps (e.g. 8) of a specified step size (e.g. −5dB), from a specified minimum value (e.g. −40 dBm) to a specifiedmaximum value (e.g. +2 dBm—where the maximum power step may be variedfrom −2 dBm to +2 dBm). If the SRC does not receive Acknowledgmentfeedbacks (ACKs) from all SNKs during any given TSF (i.e. a packet erroroccurs), it may automatically increase the PA power by the specifiedstep amount (e.g. by 5 dB). If the SRC receives a specified number (e.g.20) good TSFs in a row (which, in some embodiments, may be twenty toeighty good ACKs depending on the number of SNKs), and if the minimumReceived Signal Strength Indicator (RSSI—i.e. energy level) of the ACKsand the current SRC Transmit power is greater than a preset thresholdlevel, then it may decrease the PA power by the specified step amount.

Transmit Power Algorithm with SRC and SNK Information Exchange

The TPC algorithm shown above may facilitate saving power on the SRCside, however, it may not provide sufficiently efficient control whenTransmit power control is used on a SNK transmitter due to thetransmitter's higher PA power consumption. Hence, an alternateembodiment of the TPC algorithm may be devised to meet the requirementsas set forth above. In one set of embodiments, as part of the TPCalgorithm, SRC and SNK devices may exchange RSSI and packet receptioninformation with each other. Because SNKs may only send out an ACK whena packet is received, the SNK may only need to transmit RSSI info to theSRC while the SRC transmits RSSI and ACK reception information to theSNKs. The Source Side operation of one embodiment of an alternate TPCalgorithm is shown in a flow chart in FIG. 6, and Sink Side operation ofone embodiment of the alternate TPC algorithm is shown in a flow chartin FIG. 7. The description of the various state variables shown in FIGS.6 and 7 are respectively described in the tables shown in FIGS. 8 a and8 b.

Source Side Operation; FIGS. 6 and 8a

The algorithm may begin with initialization (602), and defining initialvalues for various variables, thresholds, Transmit power range and stepsizes, Packet/ACK counters and counter threshold (604). Following thedata turn-around (606), the SRC may start to receive ACKs from the SNKs,beginning with a first SNK (608). For Each TSF (which may not includeTSF's that are to be skipped), the SRC may include the requiredinformation on the reception of the ACKs from each SNK in the previousnon-skipped logical TSF, into the data packet to be transmitted to theSNKs (note: when using ACK first TSF timing, ACKs may be included in thesame physical TSF as the data packet). The information on each given SNKmay include whether the SRC has received the ACK from the given SNK(that is, the ‘i^(th)’ SNK), and if received, whether the RSSI levelfrom the given SNK is below the threshold level.

The SRC may set the flags (in 612) for each of the ACKs that have beencorrectly received from the corresponding SNKs (‘Yes’ branch of 610).For each of the received ACKs (‘Yes’ branch of 610), theSRC_RSSI_level_good_flag(i) may be set to 0 (in 612) if the RSSI levelis below an expected threshold, e.g. low_tx_pwr_threshold=−60 dBm). TheSNK ACK reception counter may be incremented (640) if all the ACKs havebeen correctly received and all the SNK_RSSI_level_good_flags carried inthe ACKs from the SNKs are set (path of 612, 614/616, 620, 624, 626,638, 640). Otherwise, the SNK ACK reception counter may be reset to zero(636, from the ‘No’ branch of 638). If the SNK ACK reception counter isequal to a specified Power Decrement Threshold (PDT) value, which may bea stored value having a specified default value (‘Yes’ branch of 642),the step index may be incremented by 1 (i.e. the Transmit power may bedecreased; 646 from the ‘No’ branch of 644) unless it is already at themaximum step index (‘Yes’ branch of 644). Also, the SNK ACK receptioncounter may be reset to zero (636).

If any ACKs are not received in a given TSF (‘No’ branch of 626) and theHopInX_cnt on the SRC is less than or equal to a specified value, e.g. 2on the next transmission (‘Yes’ branch of 628), then the step index maybe set to a specified value (e.g. 0) corresponding to going to maximumpower before switching channels, to try and recover the channel ifpossible (630). If any ACKs are not received in a given TSF (‘No’ branchof 626) and the HopInX_cnt is greater than the specified value on thenext transmission (‘No’ branch of 628), then the step index may bedecreased by a specified step increment, corresponding to increasing theTransmit power (634, from the ‘No’ branch of 632) unless the step indexis already at the specified value (‘Yes’ branch of 632). In either case,the SNK ACK reception counter may subsequently be reset to zero (636).To ensure HopInX is ready for the next transmission, Transmit powercontrol may continue to run after channel switching.

In one set of embodiments, a typical increment/decrement step size forthe power may be set to 5 dB when the PA power is at step 6 (0 dBm) orbelow. Furthermore, the typical increment/decrement step size may be setto be 2 dB when the PA power is above step 6. The smaller step size maybe used above the 0 dBm step to try and minimize the Transmit powerconsumption as it increases rapidly above +2 dBm.

Sink Side Operation, FIGS. 7 and 8b

Similar to the SRC side operation, the Sink side algorithm may beginwith Initialization (702), and defining initial values for variousvariables, thresholds, Transmit power range and step sizes, Packet/ACKcounters and counter threshold. For each TSF that has not been skipped,the SNK may start to receive the data packet from the SRC (704). Uponthe correct reception of the packet (‘Yes’ branch of 706), the receivedpacket RSSI level may be checked, and if the RSSI level is below anexpected specified threshold, (e.g. low_tx_pwr_threshold=−60 dBm), theSNK_RSSI_level_good_flag is set to 0, otherwise it is set to 1 (710),and the flag bit is included in the ACK sent to the SRC for SRC Transmitpower control. If the data packet from the SRC is correctly received andthe ACK detection flag from the SRC for that SNK is set (‘Yes’ branch of716), and the SRC_RSSI_level_good_flag for that SNK is set in 710,increment the SRC ACK reception counter (720, through path 706, 710,712, 714, 716, and ‘Yes’ branch of 718). Otherwise, reset the SRC ACKreception counter to zero (742, through path 706, 710, 712, 714, 716,and ‘No’ branch of 718).

If the data packet from the SRC is not received (‘No’ branch of 706), orif the data packet from the SRC is correctly received and the ACKdetection flag from the SRC for that SNK is not set (‘No’ branch of716), then the HopInX_cnt may be determined (728). If the HopInX_cnt forthat SNK is less than or equal to a specified number, e.g. 2, on thenext TSF—i.e. SRC transmission—(‘Yes’ branch of 728), the step index maybe reset to 0, corresponding to going to maximum power before switchingchannels, to try and recover the channel if possible (734), and the SRCACK reception counter may also be reset (742). To ensure HopInX is readyfor the next transmission, the Transmit power control algorithm maycontinue to run after channel switching. If the HopInX_cnt for that SNKis not less than or equal to the specified number (‘No’ branch of 728),and the step index isn't already at zero (‘No’ branch of 730), the stepindex may be decreased, e.g. by 1, corresponding to increasing theTransmit power (732). If the step index is already at 0 (‘Yes’ branch of730), the SRC ACK reception counter may be reset (742).

Subsequent to having incremented the SRC ACK reception counter in 720,if the SRC ACK reception counter is equal to the (Power DecrementThreshold) PDT (‘Yes’ branch of 722), and the step index is not alreadyat the maximum value (‘No’ branch of 724), the step index may beincremented, e.g. by 1, corresponding to decreasing the Transmit power(726). If the step index is already at the maximum value (‘Yes’ branchof 724), and also subsequent to having incremented the step index, theSRC ACK reception counter may be reset (742).

Extended Range Operation

In the embodiments shown in FIGS. 6 and 7, if extended range operationis detected, the power is simply maximized by setting the step index tothe lowest value, corresponding to increasing the Transmit power. Asseen in FIG. 6, upon detecting that either the SRC or SNK operates atextended range power (‘No’ branch of 624), the step index is set to zero(630). Similarly, in FIG. 7, upon detecting that either the SRC or SNKoperates at extended range power (‘No’ branch of 736), the step index isset to zero (734). It should be noted, that the various combinations ofstep size values, threshold values, correspondence established betweenpower level and step size, correspondence established between powerlevel and step value, and HopInX value are provided herein as examples,and various embodiments may be configured with different values andcorrespondences than what is included herein.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

1. A method for controlling transmit power, the method comprising: asource device transmitting first power information to one or more sinkdevices over a wireless Radio Frequency (RF) link; the one or more sinkdevices transmitting second power information to the source device overthe wireless RF link, comprising each of the one or more sink devicestransmitting respective second power information to the source deviceover the wireless RF link; the source device adjusting its outputtransmission power according to the second power information; and eachgiven sink device of the one or more sink devices adjusting itsrespective output transmission power according to the first powerinformation.
 2. The method of claim 1, wherein the first powerinformation comprises one or more of: Received Signal Strength Indicator(RSSI) information indicative of signal strength of signals received bythe source device, wherein the signals were transmitted by the one ormore sink devices; or packet reception information corresponding to thesource device, indicative of at least whether the source device hassuccessfully received expected packets from the one or more sinkdevices.
 3. The method of claim 2, wherein the packet receptioninformation comprises respective packet reception informationcorresponding to each given sink device of the one or more sink devices,indicative of whether the source device has successfully receivedexpected packets from the given sink device.
 4. The method of claim 1,wherein the respective second power information for any given sinkdevice of the one or more sink devices comprises Received SignalStrength Indicator (RSSI) information indicative of signal strength ofsignals received by the given sink device, wherein the signals weretransmitted by the source device.
 5. The method of claim 4, wherein thesource device adjusting its output transmission power comprises thesource device reducing its output transmission power at least inresponse to the RSSI for each given sink device indicating that thesignal strength of the signals received by the given sink device isgreater than a specified minimum value.
 6. The method of claim 4,wherein the source device adjusting its output transmission powercomprises the source device reducing its output transmission power inresponse to: the RSSI for each given sink device indicating that thesignal strength of the signals received by the given sink device isgreater than a specified minimum value; and a current source transmitpower having a value greater than a specified threshold value.
 7. Themethod of claim 4, wherein the source device adjusting its outputtransmission power comprises the source device increasing its outputtransmission power at least in response to the RSSI for at least onegiven sink device indicating that the signal strength of the signalsreceived by the given sink device is insufficiently high.
 8. The methodof claim 1, wherein the respective second power information for anygiven sink device of the one or more sink devices comprisesacknowledgment from the given sink device, indicative of the given sinkdevice having successfully received expected packets from the sourcedevice.
 9. The method of claim 8, wherein the source device adjustingits output transmission power comprises the source device reducing itsoutput transmission power at least in response to having received aspecified number of acknowledgments from each given sink device.
 10. Themethod of claim 8, further comprising the source device transmitting theacknowledgment received from each given sink device to all of the one ormore sink devices.
 11. The method of claim 1, further comprising the oneor more sink devices interrupting transmitting second power informationto the source device when the source device is not transmitting firstpower information to the one or more sink devices.
 12. The method ofclaim 1, wherein the first power information comprises respective firstpower information transmitted to each given sink device of the one ormore sink devices, wherein the respective first power informationcomprises Received Signal Strength Indicator (RSSI) informationindicative of signal strength of signals received by the source device,wherein the signals were transmitted by the given sink device.
 13. Themethod of claim 12, wherein each given sink device adjusting itsrespective output transmission power comprises the given sink devicereducing its output transmission power at least in response to the RSSIfor the source device indicating that the signal strength of the signalsreceived by the source device is greater than a specified minimum value.14. The method of claim 12, wherein each give sink device adjusting itsoutput transmission power comprises the given sink device increasing itsoutput transmission power at least in response to the RSSI for thesource device indicating that the signal strength of the signalsreceived by the source device is insufficiently high.
 15. A memorymedium configured to store programming instructions executable to:instruct a source device to adjust its output transmission poweraccording to: first power information transmitted by the source deviceto one or more sink devices over a wireless Radio Frequency (RF) link;and second power information received by the source device from the oneor more sink devices over the wireless RF link, wherein the second powerinformation comprises respective second power information for eachrespective sink device of the one or more sink devices; and instruct thesource device to retransmit the second power information to eachrespective sink device of the one or more sink devices.
 16. The memorymedium of claim 15, wherein the the first power information comprisesone or more of: Received Signal Strength Indicator (RSSI) informationindicative of signal strength of signals received by the source device,wherein the signals were transmitted by the one or more sink devices; orpacket reception information corresponding to the source device,indicative of at least whether the source device has successfullyreceived expected packets from the one or more sink devices.
 17. Thememory medium of claim 16, wherein the packet reception informationcomprises respective packet reception information corresponding to eachrespective sink device of the one or more sink devices, indicative ofwhether the source device has successfully received expected packetsfrom the respective sink device.
 18. The memory medium of claim 15,wherein the respective second power information for any respective sinkdevice of the one or more sink devices comprises Received SignalStrength Indicator (RSSI) information indicative of signal strength ofsignals received by the respective sink device, wherein the signals weretransmitted by the source device.
 19. The memory medium of claim 18,further configured to store programming instructions executable to:instruct the source device to reduce its output transmission power atleast in response to the RSSI for each respective sink device indicatingthat the signal strength of the signals received by the respective sinkdevice is greater than a specified minimum value.
 20. The memory mediumof claim 18, further configured to store programming instructionsexecutable to: instruct the source device to reduce its outputtransmission power at least in response to: the RSSI for each respectivesink device indicating that the signal strength of the signals receivedby the respective sink device is greater than a specified minimum value;and a current source transmit power having a value greater than aspecified threshold value.
 21. The memory medium of claim 18, furtherconfigured to store programming instructions executable to: instruct thesource device to increase its output transmission power at least inresponse to the RSSI for at least one respective sink device indicatingthat the signal strength of the signals received by the respective sinkdevice is insufficiently high.
 22. The memory medium of claim 15,wherein the respective second power information for any respective sinkdevice of the one or more sink devices comprises acknowledgment from therespective sink device, indicative of the respective sink device havingsuccessfully received expected packets from the source device.
 23. Thememory medium of claim 22, further configured to store programminginstructions executable to: instruct the source device to reduce itsoutput transmission power at least in response to having received aspecified number of acknowledgments from each respective sink device.24. A memory medium configured to store programming instructionsexecutable to: instruct a sink device to adjust its output transmissionpower according to first power information received from a source deviceover a wireless Radio Frequency (RF) link, wherein the first powerinformation comprises power information corresponding to the sourcedevice and one or more other sink devices operating in a multi-sinksession; and instruct the sink device to transmit second powerinformation to the source device over the wireless RF link.
 25. Thememory medium of claim 24, further configured to store programminginstructions executable to: instruct the sink device to not transmitsecond power information to the source device if the sink device has notreceived first power information from the source device.
 26. The memorymedium of claim 24, wherein the first power information comprisesReceived Signal Strength Indicator (RSSI) information indicative ofsignal strength of signals received by the source device, wherein thesignals were transmitted by the sink device.
 27. The memory medium ofclaim 26, further configured to store programming instructionsexecutable to: instruct the sink device to reduce its outputtransmission power at least in response to the RSSI corresponding to thesource device indicating that the signal strength of the signalsreceived by the source device is greater than a specified minimum value.28. The memory medium of claim 26, further configured to storeprogramming instructions executable to: instruct the sink device toincrease its output transmission power at least in response to the RSSIcorresponding to the source device indicating that the signal strengthof the signals received by the source device is insufficiently high. 29.A wireless device comprising: a transmit path comprising a poweramplifier (PA) for transmitting signals over a wireless Radio Frequency(RF) link; a receive path configured to receive signals over thewireless RF link; and a power control block configured to adjust anoutput power level of the PA according to first power information andsecond power information; wherein the wireless device is configured tocommunicate with other wireless devices over the wireless RF linkthrough the transmit path and the receive path, to transmit the firstpower information to the other wireless devices and receive the secondpower information from the other wireless devices; wherein the firstpower information comprises: information indicative of a power state ofthe wireless device; and information indicative of respective powerstates of the other wireless devices when the wireless device isoperating as a source; and wherein the second power informationcomprises information indicative of the respective power states of theother wireless devices.
 30. The wireless device of claim 29, wherein theinformation indicative of the power state of the wireless devicecomprises information indicating whether the wireless device hasreceived expected packets from the other wireless devices.
 31. Thewireless device of claim 29, wherein the information indicative of therespective power states of the other wireless devices comprisesinformation indicating whether the other wireless devices have receivedexpected packets from the wireless device.
 32. A communication systemcomprising: a source device configured to communicate with sink devicesover a wireless Radio Frequency (RF) link; and one or more sink devicesconfigured to communicate with the source device over the wireless RFlink; wherein the source device is configured to transmit first powerinformation to the one or more sink devices over the wireless RF link;wherein each respective sink device of the one or more sink devices isconfigured to transmit respective second power information to the sourcedevice over the wireless RF link; wherein the source device is furtherconfigured to adjust its output transmission power according to thesecond power information; and wherein each respective sink device isconfigured to adjust its respective output transmission power accordingto the first power information.
 33. The communication system of claim32, wherein the first power information comprises the respective powerinformation received by the source device from each respective sinkdevice, wherein the source device is configured to transmit the firstpower information to all of the one or more sink devices.